scholarly journals The Bacteriophage T4 Inhibitor and Coactivator AsiA Inhibits Escherichia coli RNA Polymerase More Rapidly in the Absence of σ70 Region 1.1: Evidence that Region 1.1 Stabilizes the Interaction between σ70 and Core

2006 ◽  
Vol 188 (4) ◽  
pp. 1279-1285 ◽  
Author(s):  
Deborah M. Hinton ◽  
Srilatha Vuthoori ◽  
Rebecca Mulamba
Keyword(s):  
Escherichia Coli ◽  
Dna Binding ◽  
Rna Polymerase ◽  
Dynamic Equilibrium ◽  
Bacteriophage T4 ◽  
Direct Interaction ◽  
Binding Properties ◽  
E Coli ◽  
Dna Binding Properties ◽  
Two Hybrid

ABSTRACT The N-terminal region (region 1.1) of σ70, the primary σ subunit of Escherichia coli RNA polymerase, is a negatively charged domain that affects the DNA binding properties of σ70 regions 2 and 4. Region 1.1 prevents the interaction of free σ70 with DNA and modulates the formation of stable (open) polymerase/promoter complexes at certain promoters. The bacteriophage T4 AsiA protein is an inhibitor of σ70-dependent transcription from promoters that require an interaction between σ70 region 4 and the −35 DNA element and is the coactivator of transcription at T4 MotA-dependent promoters. Like AsiA, the T4 activator MotA also interacts with σ70 region 4. We have investigated the effect of region 1.1 on AsiA inhibition and MotA/AsiA activation. We show that σ70 region 1.1 is not required for MotA/AsiA activation at the T4 middle promoter P uvsX . However, the rate of AsiA inhibition and of MotA/AsiA activation of polymerase is significantly increased when region 1.1 is missing. We also find that RNA polymerase reconstituted with σ70 that lacks region 1.1 is less stable than polymerase with full-length σ70. Our previous work has demonstrated that the AsiA-inhibited polymerase is formed when AsiA binds to region 4 of free σ70 and then the AsiA/σ70 complex binds to core. Our results suggest that in the absence of region 1.1, there is a shift in the dynamic equilibrium between polymerase holoenzyme and free σ70 plus core, yielding more free σ70 at any given time. Thus, the rate of AsiA inhibition and AsiA/MotA activation increases when RNA polymerase lacks region 1.1 because of the increased availability of free σ70. Previous work has argued both for and against a direct interaction between regions 1.1 and 4. Using an E. coli two-hybrid assay, we do not detect an interaction between these regions. This result supports the idea that the ability of region 1.1 to prevent DNA binding by free σ70 arises through an indirect effect.

scholarly journals The Bacteriophage T4 Transcription Activator MotA Interacts with the Far-C-Terminal Region of the σ70 Subunit of Escherichia coli RNA Polymerase

2002 ◽  
Vol 184 (14) ◽  
pp. 3957-3964 ◽  
Author(s):  
Suchira Pande ◽  
Anna Makela ◽  
Simon L. Dove ◽  
Bryce E. Nickels ◽  
Ann Hochschild ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Rna Polymerase ◽  
Bacteriophage T4 ◽  
In Vitro Transcription ◽  
Terminal Region ◽  
Transcription Activator ◽  
E Coli ◽  
Terminal Amino ◽  
Two Hybrid

ABSTRACT Transcription from bacteriophage T4 middle promoters uses Escherichia coli RNA polymerase together with the T4 transcriptional activator MotA and the T4 coactivator AsiA. AsiA binds tightly within the C-terminal portion of the σ70 subunit of RNA polymerase, while MotA binds to the 9-bp MotA box motif, which is centered at −30, and also interacts with σ70. We show here that the N-terminal half of MotA (MotANTD), which is thought to include the activation domain, interacts with the C-terminal region of σ70 in an E. coli two-hybrid assay. Replacement of the C-terminal 17 residues of σ70 with comparable σ38 residues abolishes the interaction with MotANTD in this assay, as does the introduction of the amino acid substitution R608C. Furthermore, in vitro transcription experiments indicate that a polymerase reconstituted with a σ70 that lacks C-terminal amino acids 604 to 613 or 608 to 613 is defective for MotA-dependent activation. We also show that a proteolyzed fragment of MotA that contains the C-terminal half (MotACTD) binds DNA with a K D(app) that is similar to that of full-length MotA. Our results support a model for MotA-dependent activation in which protein-protein contact between DNA-bound MotA and the far-C-terminal region of σ70 helps to substitute functionally for an interaction between σ70 and a promoter −35 element.

scholarly journals Probing E. coli SSB Protein-DNA topology by reversing DNA backbone polarity

2020 ◽  
Author(s):  
Alexander G. Kozlov ◽  
Timothy M. Lohman
Keyword(s):  
Dna Binding ◽  
Crystal Structures ◽  
Nearest Neighbor ◽  
Genome Maintenance ◽  
Binding Properties ◽  
Ssdna Binding ◽  
E Coli ◽  
Phosphodiester Linkage ◽  
The Individual ◽  
Dna Binding Properties

AbstractE. coli single strand (ss) DNA binding protein (SSB) is an essential protein that binds ssDNA intermediates formed during genome maintenance. SSB homo-tetramers bind ssDNA in two major modes differing in occluded site size and cooperativity. The (SSB)35 mode in which ssDNA wraps on average around two subunits is favored at low [NaCl] and high SSB to DNA ratios and displays high “unlimited”, nearest-neighbor cooperativity forming long protein clusters. The (SSB)65 mode, in which ssDNA wraps completely around four subunits of the tetramer, is favored at higher [NaCl] (> 200 mM) and displays “limited” low cooperativity. Crystal structures of E. coli SSB and P. falciparum SSB show ssDNA bound to the SSB subunits (OB-folds) with opposite polarities of the sugar phosphate backbones. To investigate whether SSB subunits show a polarity preference for binding ssDNA, we examined EcSSB and PfSSB binding to a series of (dT)70 constructs in which the backbone polarity was switched in the middle of the DNA by incorporating a reverse polarity (RP) phosphodiester linkage, either 3’-3’ or 5’-5’. We find only minor effects on the DNA binding properties for these RP constructs, although (dT)70 with a 3’-3’ polarity switch shows decreased affinity for EcSSB in the (SSB)65 mode and lower cooperativity in the (SSB)35 mode. However, (dT)70 in which every phosphodiester linkage is reversed, does not form a completely wrapped (SSB)65 mode, but rather binds EcSSB in the (SSB)35 mode, with little cooperativity. In contrast, PfSSB, which binds ssDNA only in an (SSB)65 mode and with opposite backbone polarity and different topology, shows little effect of backbone polarity on its DNA binding properties. We present structural models suggesting that strict backbone polarity can be maintained for ssDNA binding to the individual OB-folds if there is a change in ssDNA wrapping topology of the RP ssDNA.Statement of SignificanceSingle stranded (ss) DNA binding (SSB) proteins are essential for genome maintenance. Usually homo-tetrameric, bacterial SSBs bind ssDNA in multiple modes, one of which involves wrapping 65 nucleotides of ssDNA around all four subunits. Crystal structures of E. coli and P. falciparum SSB-ssDNA complexes show ssDNA bound with different backbone polarity orientations raising the question of whether these SSBs maintain strict backbone polarity in binding ssDNA. We show that both E. coli and P. falciparum SSBs can still form high affinity fully wrapped complexes with non-natural DNA containing internal reversals of the backbone polarity. These results suggest that both proteins maintain a strict backbone polarity preference, but adopt an alternate ssDNA wrapping topology.

scholarly journals Bacterial Two-Hybrid Analysis of Interactions between Region 4 of the ς70 Subunit of RNA Polymerase and the Transcriptional Regulators Rsd from Escherichia coli and AlgQ from Pseudomonas aeruginosa

2001 ◽  
Vol 183 (21) ◽  
pp. 6413-6421 ◽  
Author(s):  
Simon L. Dove ◽  
Ann Hochschild
Keyword(s):  
Gene Expression ◽  
Escherichia Coli ◽  
Pseudomonas Aeruginosa ◽  
Amino Acid ◽  
Rna Polymerase ◽  
Amino Acid Substitution ◽  
Transcriptional Regulators ◽  
Binding Motif ◽  
E Coli ◽  
Two Hybrid

ABSTRACT A number of transcriptional regulators mediate their effects through direct contact with the ς70 subunit ofEscherichia coli RNA polymerase (RNAP). In particular, several regulators have been shown to contact a C-terminal portion of ς70 that harbors conserved region 4. This region of ς contains a putative helix-turn-helix DNA-binding motif that contacts the −35 element of ς70-dependent promoters directly. Here we report the use of a recently developed bacterial two-hybrid system to study the interaction between the putative anti-ς factor Rsd and the ς70 subunit of E. coli RNAP. Using this system, we found that Rsd can interact with an 86-amino-acid C-terminal fragment of ς70 and also that amino acid substitution R596H, within region 4 of ς70, weakens this interaction. We demonstrated the specificity of this effect by showing that substitution R596H does not weaken the interaction between ς and two other regulators shown previously to contact region 4 of ς70. We also demonstrated that AlgQ, a homolog of Rsd that positively regulates virulence gene expression inPseudomonas aeruginosa, can contact the C-terminal region of the ς70 subunit of RNAP from this organism. We found that amino acid substitution R600H in ς70 fromP. aeruginosa, corresponding to the R596H substitution in E. coli ς70, specifically weakens the interaction between AlgQ and ς70. Taken together, our findings suggest that Rsd and AlgQ contact similar surfaces of RNAP present in region 4 of ς70 and probably regulate gene expression through this contact.

DNA-binding properties of nuclear matrix proteins

1978 ◽  
Vol 34 (1) ◽  
pp. 233-246 ◽  
Author(s):  
D.E. Comings ◽  
A.S. Wallack
Keyword(s):  
Dna Binding ◽  
Nuclear Matrix ◽  
Matrix Proteins ◽  
Binding Properties ◽  
E Coli ◽  
Nuclear Matrix Proteins ◽  
The Matrix ◽  
Filter Assay ◽  
Dna Binding Properties ◽  
Competition Assays

Mouse nuclear matrix proteins, examined by a filter assay, were found to bind to DNA. There was no preference for homologous mouse compared to heterologous E. coli DNA. Competition assays showed a preference for AT-rich DNA and of the 4 single-stranded homopolymers there was a preference for poly(dT). These observations are consistent with the possibility that the matrix may play a role in the formation of AT-rich chromomeres (G-bands).

scholarly journals A Mutation within the β Subunit of Escherichia coli RNA Polymerase Impairs Transcription from Bacteriophage T4 Middle Promoters

2010 ◽  
Vol 192 (21) ◽  
pp. 5580-5587 ◽  
Author(s):  
Tamara D. James ◽  
Michael Cashel ◽  
Deborah M. Hinton
Keyword(s):  
Escherichia Coli ◽  
Rna Polymerase ◽  
Bacteriophage T4 ◽  
Β Subunit ◽  
Subunit Gene ◽  
Wild Type ◽  
Promoter Activation ◽  
E Coli ◽  
Growth Phenotype

ABSTRACT During infection of Escherichia coli, bacteriophage T4 usurps the host transcriptional machinery, redirecting it to the expression of early, middle, and late phage genes. Middle genes, whose expression begins about 1 min postinfection, are transcribed both from the extension of early RNA into middle genes and by the activation of T4 middle promoters. Middle-promoter activation requires the T4 transcriptional activator MotA and coactivator AsiA, which are known to interact with σ70, the specificity subunit of RNA polymerase. T4 motA amber [motA(Am)] or asiA(Am) phage grows poorly in wild-type E. coli. However, previous work has found that T4 motA(Am)does not grow in the E. coli mutant strain TabG. We show here that the RNA polymerase in TabG contains two mutations within its β-subunit gene: rpoB(E835K) and rpoB(G1249D). We find that the G1249D mutation is responsible for restricting the growth of either T4 motA(Am)or asiA(Am) and for impairing transcription from MotA/AsiA-activated middle promoters in vivo. With one exception, transcription from tested T4 early promoters is either unaffected or, in some cases, even increases, and there is no significant growth phenotype for the rpoB(E835K G1249D) strain in the absence of T4 infection. In reported structures of thermophilic RNA polymerase, the G1249 residue is located immediately adjacent to a hydrophobic pocket, called the switch 3 loop. This loop is thought to aid in the separation of the RNA from the DNA-RNA hybrid as RNA enters the RNA exit channel. Our results suggest that the presence of MotA and AsiA may impair the function of this loop or that this portion of the β subunit may influence interactions among MotA, AsiA, and RNA polymerase.

scholarly journals Differential Mechanisms of Binding of Anti-Sigma Factors Escherichia coli Rsd and Bacteriophage T4 AsiA to E. coli RNA Polymerase Lead to Diverse Physiological Consequences

2008 ◽  
Vol 190 (10) ◽  
pp. 3434-3443 ◽  
Author(s):  
Umender K. Sharma ◽  
Dipankar Chatterji
Keyword(s):  
Escherichia Coli ◽  
Cell Growth ◽  
Rna Polymerase ◽  
Bacteriophage T4 ◽  
Sigma Factors ◽  
E Coli ◽  
Yeast Two Hybrid System ◽  
Vitro Binding

ABSTRACT Anti-sigma factors Escherichia coli Rsd and bacteriophage T4 AsiA bind to the essential housekeeping sigma factor, σ70, of E. coli. Though both factors are known to interact with the C-terminal region of σ70, the physiological consequences of these interactions are very different. This study was undertaken for the purpose of deciphering the mechanisms by which E. coli Rsd and bacteriophage T4 AsiA inhibit or modulate the activity of E. coli RNA polymerase, which leads to the inhibition of E. coli cell growth to different amounts. It was found that AsiA is the more potent inhibitor of in vivo transcription and thus causes higher inhibition of E. coli cell growth. Measurements of affinity constants by surface plasmon resonance experiments showed that Rsd and AsiA bind to σ70 with similar affinity. Data obtained from in vivo and in vitro binding experiments clearly demonstrated that the major difference between AsiA and Rsd is the ability of AsiA to form a stable ternary complex with RNA polymerase. The binding patterns of AsiA and Rsd with σ70 studied by using the yeast two-hybrid system revealed that region 4 of σ70 is involved in binding to both of these anti-sigma factors; however, Rsd interacts with other regions of σ70 as well. Taken together, these results suggest that the higher inhibition of E. coli growth by AsiA expression is probably due to the ability of the AsiA protein to trap the holoenzyme RNA polymerase rather than its higher binding affinity to σ70.

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